The present disclosure generally relates to water remediation and management, and, more specifically, to methods in which the presence of various metal ions in a metal-laden water is mitigated.
Treatment fluids can be used in a variety of subterranean treatment operations. Such treatment operations can include, without limitation, drilling operations, stimulation operations, production operations, remediation operations, sand control treatments, and the like. As used herein, the terms “treat,” “treatment,” “treating,” and grammatical equivalents thereof refer to any subterranean operation that uses a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid or a component thereof, unless otherwise specified herein. More specific examples of illustrative treatment operations can include, for example, drilling operations, fracturing operations, gravel packing operations, acidizing operations, scale dissolution and removal operations, sand control operations, consolidation operations, and the like.
Many types of subterranean treatment operations use treatment fluids containing a continuous phase that is “viscosified” or “gelled.” These terms will be used synonymously herein. In illustrative examples, gelled fluids may be used in fracturing operations, gravel packing operations, fluid diversion and fluid loss control operations, well kills, and the like. Common gelling agents can include viscoelastic surfactants and viscosifying polymers, including polymers that are crosslinked with a crosslinking agent. Polymeric gelling agents can include biopolymers or synthetic polymers. Gellable synthetic polymers can include acrylamide polymers, copolymers and their derivatives, for example. A multitude of gellable biopolymers and biopolymer derivatives are known in the art. Biopolymers and their derivatives may be particularly desirable in subterranean treatment operations due to their degradation into environmentally benign byproducts over time. Gelled fluids may be further classified as described below in reference to fracturing fluids.
Although non-crosslinked polymers may increase the viscosity of a fluid, a more pronounced viscosity increase may be obtained upon crosslinking adjacent polymer chains. A variety of crosslinking agents are available for forming a crosslinked polymer. Depending upon a number of factors such as, for example, the chemical and physical conditions to which a fluid subject to gelation is to be exposed, the desired time to gelation, the desired gel strength and gel stability, and the like, a particular class of crosslinking agent may be chosen for use in conjunction with a given gellable polymer to best accomplish the gel's intended purpose. Polyalkyleneimines and polyalkylenepolyamines are organic crosslinking agents that may be used to form a gelled polymer, particularly with acrylamide polymers and their derivatives. Transition metal ions (e.g., chromium, vanadium, titanium, zirconium, and the like) and main group metal ions (e.g., aluminum, antimony, tin, and the like) may also be used to affect crosslinking in the course of forming a gelled fluid. Metal ion crosslinking agents often function most effectively in a circumneutral to modestly acidic pH range, such as a pH of about 4.5 to about 8. At modestly basic pH values, such as pH values above about 8.5, boric acid, boronic acid and borate crosslinking agents may also be used to affect crosslinking.
Fracturing fluids and gravel packing fluids are often viscosified in order to provide the fluid with sufficient capability to convey particulate matter (e.g., proppant particulates or gravel particulates) into a wellbore. Water frac or “slickwater” fracturing operations are run at high pump rates using a fluid phase containing a relatively low concentration of a non-crosslinked acrylamide polymer or copolymer. Linear gels with higher viscosities may be formed at increased polymer concentrations, particularly when using a non-crosslinked biopolymer or an incompletely crosslinked biopolymer. Linear gels remain flowable and are frequently used in fracturing operations and gravel packing operations. Even higher fluid viscosities may be obtained by extensively crosslinking the biopolymers of linear gels with metal ions, thereby forming a crosslinked gel. Crosslinked gels are much more difficult to flow due to their higher viscosity values. Although crosslinked gels may be used in fracturing operations, they have a higher propensity to promote subterranean formation damage than do linear gels and they require even higher pump rates.
In some cases, it can be desirable to form a crosslinked gel within a subterranean formation. For example, it may sometimes be desirable to form a temporary or permanent fluid seal within a wellbore using a crosslinked gel. However, if the formation of a crosslinked gel occurs unexpectedly or in an improper location within a wellbore, for example, the situation can be very difficult to address and may necessitate a remediation operation. In illustrative examples, unwanted gelation may occur upon the gelling agent encountering higher than expected temperature conditions or inadvertently contacting extraneous crosslinking metal ions. Unwanted contact of a gelling agent with crosslinking metal ions can preclude the use of some types of water for forming a viscosified fluid, as discussed hereinafter.
Water conservation and management are becoming increasingly important concerns for the oilfield industry. On the treatment side of subterranean operations, immense volumes of water (millions of gallons per well) are used in the course of drilling, treating and producing a wellbore. Sourcing and transportation requirements for the water can represent a significant cost liability. On the production side, at least a portion of the introduced water may be subsequently produced from the wellbore in the course of producing a desired hydrocarbon resource, such as oil. Groundwater may also be produced from a wellbore in conjunction with a hydrocarbon resource. Increasingly strict environmental regulations have made disposal of produced treatment fluids, produced groundwater and other process water sources a significant issue. The complex chemical nature of produced water and other process water sources often necessitates long-term storage of the water while awaiting chemical analyses, and oftentimes remediation to make the produced water suitable for disposal. These factors can significantly expand the required infrastructure at a job site and increase the time and expense needed for producing a hydrocarbon resource from a subterranean formation. Of particular note, a multitude of metal ions of varying types may be present in produced water and other process water sources, which may be difficult to remediate effectively due to the chemical complexity of potentially interfering metal ions. Organic constituents may also be present in the produced water, alone or in combination with metal ions.